The magnetic particle testing method (MT) is one of the most sensitive, reliable and productive NDT-methods for surface inspection of products from ferromagnetic materials. The method is based on the attraction of ferromagnetic particles by force of leakage flux which appears above surface defects like cracks, laps, lacks of fusion, pores after an adequate magnetization. MT can be used for indication of open surface defects and under certain conditions for detection of near-surface defects. A higher probability of detection is given, when the direction of a defect is perpendicular to the direction of the applied magnetic field. The smaller is the angle between the defect and magnetic field lines, the weaker is the indication.

The magnetic particle testing is a separate processing procedure which consists of following parts: